Dielectric ceramic material

ABSTRACT

Disclosed is a dielectric ceramic material represented by composition formula: (uLi 2 O—vNa 2 O)—wSm 2 O 3 —xCaO—yTiO 2 , having a solid solution structure made up of perovskite crystals represented by Ca 1−x Sm 2x/3 TiO 3 , perovskite crystals represented by Li 1/2 Sm 1/2 TiO 3 , and perovskite crystals represented by Na 1/2 Sm 1/2 TiO 3 . Substitution of part of Ti in the composition with at least one of Ga and Al provides a dielectric ceramic material with a particularly increased value of unloaded quality coefficient. The absolute value of the temperature coefficient of resonance frequency is controlled to a small value by adjusting the proportions of Li and Na.

BACKGROUND OF THE INVENTION

1. Field of the invention

This invention relates to a dielectric ceramic material. More particularly, it relates to a dielectric ceramic material which exhibits excellent dielectric characteristics, i.e., a high relative dielectric constant (hereinafter represented by ∈_(r)) in a high frequency region, a high unloaded quality coefficient (hereinafter represented by Q_(u)), and a small absolute value of the temperature coefficient of resonance frequency (hereinafter resonance frequency is represented by f₀, and the temperature coefficient thereof is represented by τ_(f)). The dielectric ceramic material of the present invention is suited for use in multilayer circuit boards, resonators and filters particularly for use in a high frequency region, an impedance matching element for various microwave circuits, and the like.

2. Description of the Related Art

With the recent increase of communication information, rapid progress is being made in various communication systems utilizing the microwave region, such as mobile telecommunication systems, satellite communication systems, positioning systems using communication data, and satellite broadcasting. Use of the communication systems in a submillimeter wave region has been demanded. Many dielectric materials have been developed with the rapid progress. These dielectric materials are required to have (1) a high relative dielectric constant ∈_(r), (2) a high unloaded quality coefficient Q_(u) (i.e., a small dielectric loss 1/Q_(u)), and (3) a small absolute value of τ_(f) (i.e., small temperature dependence of f₀).

In particular, a dielectric material used in a submillimeter wave region is required to have an especially high Q_(u), and it is desirable that τ_(f) be controllable freely around 0 ppm/° C.

Microwave dielectric porcelain compositions based on Li₂O—CaO—Sm₂O₃—TiO₂ are disclosed in JP-A-5-211007 and JP-A-5-211009. These materials have a particularly excellent ∈_(r) value but a relatively small Q_(u). While the τ_(f) is relatively controlled by the composition, the precise control has been difficult, and control to nearly 0 ppm/° C. has not been realized as yet.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a dielectric ceramic material which has a high Q_(u) value even in a submillimeter wave region, can have its τ_(f) controlled around 0 ppm/° C., and exhibits a high ∈_(r) value.

The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has been claimed in the present application is incorporated herein by reference, as if fully set forth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a dielectric filter utilizing the dielectric material of the present invention, and

FIG. 1B is a front view taken from the open end surface of FIG. 1A.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a dielectric ceramic material represented by composition formula: (uLi₂O—vNa₂O)—wSm₂O₃—xCaO—yTiO₂, wherein u+v+w+x+y=100 mol %, 0<u<40, 0<v<40, 0<u+v≦40, 0<w≦30, 0<x≦40, and 0<y≦80 (hereinafter referred to as dielectric ceramic material A).

The present invention also provides a dielectric ceramic material represented by composition formula: (uLi₂O—vNa₂O)—wSm₂O₃—xCaO—(yTiO₂—zM₂O₃), wherein M represents Ga or Al; u+v+w+x+y+z=100 mol %, 0≦u≦40, 0≦v≦40, 0<u+v≦40, 0<w≦30, and 0<x≦40, 0<y<80, 0<z<80, and 0<y+z≦80 (hereinafter referred to as dielectric ceramic material B).

In dielectric ceramic material A, the molar ratio of the Li oxide (u) and that of the Na oxide (v) satisfy 0<u<40 and 0<v<40, respectively. That is, dielectric ceramic material A contains both Li oxide and Na oxide. The total molar ratio of the Na oxide and the Li oxide (i.e., u+v) satisfies 0<u+v≦40, preferably 3≦u+v≦15, still preferably 5≦u+v≦8.

It is preferred that u and v satisfy 3≦u<40 and 0<v≦30. When u and v satisfy this ranges, it is preferred in the point that τ_(f) is not greatly shifted to the plus side.

In dielectric ceramic material B, the molar ratio of Li oxide (u) and that of Na oxide (v) satisfy 0≦u≦40 and 0≦v≦40, respectively, and the total molar ratio of the Li oxide and the Na oxide (u+v) satisfies 0<u+v≦40. That is, dielectric ceramic material B contains at least one of Li oxide and Na oxide. The total molar ratio u+v is preferably equal to or greater than 3 and equal to or smaller than 15, still preferably equal to or greater than 5 and equal to or smaller than 8.

It is preferred that u and v satisfy 3≦u≦40 and 0≦v≦30. When u and v satisfy this ranges, it is preferred in the point that τ_(f) is not greatly shifted to the plus side.

According to the desired dielectric characteristics, Li oxide may be excluded from the composition in dielectric ceramic material B.

If dielectric ceramic materials A and B contain excessive Li oxide and Na oxide, Q_(u)xf₀ tends to be small.

The molar ratio of Sm oxide (w) in dielectric ceramic materials A and B satisfies 0<w≦30, preferably 8≦w≦20, still preferably 10<w≦16. Where Sm oxide is present in excess, ∈_(r) tends to be reduced.

The molar ratio of Ca oxide (x) in dielectric ceramic materials A and B satisfies 0<x≦40, preferably 5<x≦30, still preferably 9<x≦18. Where Ca oxide is present in excess, τ_(f) tends to be greatly shifted to the plus side.

The molar ratio of Ti oxide (y) in dielectric ceramic material A satisfies 0<y≦80, preferably 30≦y≦77, still preferably 50≦y≦75.

The molar ratio of Ti oxide (y) and that of at least one of Ga and Al oxides (z) in dielectric ceramic material B satisfy 0<y<80 and 0<z<80. That is, dielectric ceramic material B has part of Ti displaced with at least one of Ga and Al to contain at least one of Ga oxide and Al oxide. The total molar ratio of Ti oxide and at least one of Ga and Al oxides (i.e., y+z) satisfies 0<y+z≦80, preferably 30≦y+z≦75, still preferably 60≦y+z≦70.

If the dielectric ceramic material B contains Ti oxide and Ga or Al oxide in excessive amounts, ∈_(r) tend to be low.

Q_(u)xf₀ increases with the ratio of z to y in (yTiO₂—zM₂O₃), i.e., the degree of substitution of Ti with at least one of Ga and Al. However, if the degree of substitution exceeds 50 mol % based on the Ti oxide, ∈_(r) tends to decrease due to phase separation or change of the crystal structure. Accordingly, it is preferred that 40≦y<80 and 0≦z<40, particularly 30≦y≦60 and 3≦z≦35.

In the present invention, where 5≦u+v≦20, a ∈_(r) value of 75 or greater and Q_(u)xf₀ of 6000 GHz or greater can be secured. In particular where u, v, w, x, and y satisfy 5≦u≦7, 1≦v≦3, 12≦w≦14, 12≦x≦18, and 60≦y≦65, ∈_(r) of 99 or greater, Q_(u)xf₀ of 6100 GHz or greater, and τ_(f) of −9 to 12 ppm/° C. can be secured.

Further, where 4≦u≦8, 0≦v≦3, 12≦w≦15, 16≦x≦19, 32≦y≦35, and 28≦z≦32, it is possible to obtain ∈_(r) of 58 or greater and Q_(u)xf₀ of 10080 GHz or greater.

It has been known that many dielectric materials having a perovskite structure exhibit excellent dielectric characteristics. The dielectric ceramic material according to the present invention is considered to be a solid solution structure made up of Ca_(1−x)Sm_(2x/3)TiO₃ that has a perovskite structure and exhibits a very high ∈_(r) value, a large Q_(u)xf₀ value, and a positive τ_(f) value; Li_(1/2)Sm_(1/2)TiO₃ that has a perovskite structure and exhibits a high ∈_(r) value and a large τ_(f) value in the minus side; and Na_(1/2)Sm_(1/2)TiO₃ that has a perovskite structure and exhibits a large Q_(u)xf₀ value and a large τ_(f) value in the plus side. The excellent dielectric characteristics of the ceramic material of the invention seems attributed to this structure. Where the dielectric ceramic material of the invention has such a solid solution composition or a nearly solid solution composition, it is possible to obtain ∈_(r) of nearly 100, Q_(u)xf₀ of about 6000 GHz, and τ_(f) of around 0 ppm/° C. Where part of Ti⁴⁺ contained in the structure is replaced with at least one of Ga³⁺ and Al³⁺, whose ionic radius is relatively close to that of Ti⁴⁺ and whose valence is different from that of Ti by +1, Q_(u)xf₀ is improved. Further, the value of τ_(f) can be controlled by varying the proportions of Li oxide and Na oxide, which exhibit τ_(f) values of opposite signs.

EXAMPLES

The present invention will now be illustrated in greater detail by way of Examples.

Predetermined amounts of commercially available powders of Li₂CO₃ (purity: 99%), Na₂CO₃ (purity: 99%), Sm₂O₃ (purity: 99.9%, D50: 1.9 μm), CaCO₃ (purity: 99.9%, D50: 2.6 μm), TiO₂ (purity: 99%, Average particle size: 0.25 μm) , Al₂O₃ (purity: 99.9%, Particle size: 2 to 3 μm) and Ga₂O₃ (purity: 99.9%) were weighed out (100 g in total) to give the final composition shown in Tables 1 and 2 below in terms of the respective oxides.

The powders were wet mixed in a ball mill for 15 hours using ethanol as a medium, and the resulting slurry was dried on a hot water bath and calcined in the air atmosphere at 1000° C. for 2 hours. The calcined product was wet ground for 15 hours in a ball mill together with a wax binder, a dispersant, and ethanol. The resulting slurry was dried on a hot water bath, granulated and compacted under a pressure of 10 MPa into a rod form of 20 mm in diameter and 12 mm in thickness. The rod compact was subjected to cold isostatic pressing (CIP) under a pressure of 150 MPa, and then sintered by firing at 1300° C. for 5 hours in the air atmosphere to obtain a sintered body.

After surface of the resulting sintered body, i.e., a dielectric material, was ground with a #200 diamond, ∈_(r), Q_(u), and τ_(f) were measured by the Hakki and Coleman's method in a measuring frequency range of from 1 to 3 GHz at a measuring temperature of from 25 to 80° C. The τ_(f) value was calculated according to equation: τ_(f)=(f₈₀−f₂₅)/{(f₂₅×(80−25)}×10⁶, wherein f₂₅ is a resonance frequency at 25° C., and f₈₀ is a resonance frequency at 80° C.

The results obtained are shown in Tables 1 and 2.

TABLE 1 Dielectric Characteristics Run Composition Q_(u)xf₀ τ_(f) No. u v w x y ε_(r) (GHZ) (ppm/° C.) Remark 1 3 3 33 6 56 31 4890 91 comparison 2 3 3 15 10 69 79 6200 1 invention 3 4 2 15 10 69 78 6180 −10 ″ 4 3 4 15 10 69 79 6270 8 ″ 5 7 1 13 16 63 99 6110 −9 ″ 6 6 2 13 16 63 99 6140 2 ″ 7 5 3 13 16 63 99 6180 12 ″ 8 3 12 11 16 59 88 6050 112 ″ 9 25 20 15 15 20 85 3070 66 comparison

TABLE 2 Composition Dielectric Characteristics Run z Q_(u)xf₀ τ_(f) No. u v w x y Ga₂O₃ Al₂O₃ ε_(r) (GHZ) (ppm/° C.) Remark 10 7 — 13 17 58 5 — 89 7200 −11 invention 11 6 1 13 17 53 10 — 80 7940 0 ″ 12 7 — 13 17 53 10 — 80 7810 −16 ″ 13 7 — 13 17 43 20 — 71 9340 −12 ″ 14 6 — 14 16 44 20 — 70 9760 −22 ″ 15 6 1 13 17 33 30 — 59 12030 1 ″ 16 7 — 13 17 33 30 — 58 11700 −10 ″ 17 6 2 13 16 3 60 — 37 8750 65 ″ 18 3 2 2 3 5 85 — 22 3420 72 comparison 19 6 1 15 15 58 — 5 78 6900 2 invention 20 6 1 15 15 53 — 10 75 7350 1 ″ 21 7 — 13 17 43 — 20 69 8060 20 ″ 22 5 — 14 18 34 — 30 59 10080 30 ″ 23 6 1 10 10 13 — 60 35 8340 61 ″ 24 3 2 2 3 5 — 85 21 3190 69 comparison

The results in Table 1 prove that τ_(f) is controllable by adjusting the proportions of the alkali metal oxides, i.e., Li₂O and Na₂O in dielectric ceramic material A (Run Nos. 2 to 8).

The results in Table 2 prove that the Q_(u)xf₀ value increases to 7200 to 12030 GHz with an increase in degree of substitution of Ti with Ga (Run Nos. 10 to 17) and increases to 6900 to 10800 GHz with an increase in degree of substitution of Ti with Al (Run Nos. 19 to 23). It can be seen accordingly that the Q_(u)xf₀ value can be controlled by substituting Ti with at least one of Ga and Al.

(1) A First Example of Dielectric Filter Prepared by Using Dielectric Material of the Invention

The dielectric material of the present invention may be used in a dielectric filter described in U.S. Pat. No. 5,612,654, hereby incorporated by reference.

For example, the dielectric filter shown in FIGS. 1A and 1B includes resonator holes 202 a and 202 b.

In the structure shown in FIGS. 1A and 1B, the coupling between the two resonators formed at resonator holes 202 a and 202 b is inductive coupling, and one attenuation pole is formed in the high frequency range of the pass band. A pair of input/output electrodes 205 are formed at prescribed portions on the outer surface of dielectric block 201. Inner conductors 203 are formed on the inner surfaces of resonator holes 202 a and 202 b.

While the invention has been described in detail and with reference to specific examples thereof, various changes and modifications can be made within the scope thereof according to the final use. That is, the dielectric ceramic materials may contain other components or unavoidable impurities as long as the dielectric characteristics are not substantially affected thereby.

The dielectric ceramic material having composition formula: (uLi₂O—vNa₂O)—wSm₂O₃—xCaO—yTiO₂ exhibits excellent dielectric characteristics. Q_(u)xf₀ can be controlled in a range of large values by substituting Ti in the composition formula with Ga or Al. Further, the value τ_(f) is controllable by adjusting the proportions of Li and Na. 

What is claimed is:
 1. A dielectric ceramic material represented by the composition formula: (uLi₂O—vNa₂O)—wSm₂O₃—xCaO—(yTiO₂—zM₂O₃), wherein M represents at least one of Ga and Al; u+v+w+x+y+z=100 mol %, 0≦u≦40, 0≦v≦40, 0<u+v≦40, 0<w≦30, 0<x≦40, 0<y<80, 0<z<80, and 0<y+z≦80.
 2. A dielectric ceramic material according to claim 1, wherein 3≦u≦40, and 0≦v≦30.
 3. A dielectric ceramic material according to claim 1, wherein 40≦y<80, and 0≦z<40.
 4. A dielectric ceramic material according to claim 2, wherein 40≦y<80, and 0≦z<40.
 5. A dielectric ceramic material according to claim 1, wherein M represents Ga.
 6. A dielectric ceramic material according to claim 1, wherein M represents Al.
 7. A dielectric ceramic material according to claim 1, wherein 3≦u+v≦15.
 8. A dielectric ceramic material according to claim 1, wherein 5≦u+v≦8.
 9. A dielectric ceramic material according to claim 1, wherein 8≦w≦20.
 10. A dielectric ceramic material according to claim 1, wherein 10<w≦16.
 11. A dielectric ceramic material according to claim 1, wherein 5<x≦30.
 12. A dielectric ceramic material according to claim 1, wherein 9<x≦18.
 13. A dielectric ceramic material according to claim 1, wherein 30≦y+z≦75.
 14. A dielectric ceramic material according to claim 1, wherein 60≦y+z≦70.
 15. A dielectric ceramic material according to claim 1, wherein 30≦y≦60 and 3≦z≦35.
 16. A dielectric filter comprising a dielectric ceramic material according to claim
 1. 17. A dielectric ceramic material according to claim 1, wherein 4≦u≦8, 0≦v≦3, 12≦w≦15, 16≦x≦19, 32≦y≦35 and 28≦z≦32.
 18. A dielectric ceramic material according to claim 1, wherein 5≦z≦80.
 19. A dielectric ceramic material according to claim 1, wherein 10≦z≦80.
 20. A dielectric ceramic material according to claim 1, wherein 20≦z≦80.
 21. A dielectric ceramic material according to claim 1, wherein 30≦z≦80.
 22. A dielectric ceramic material according to claim 1, wherein 60≦z≦80. 